An alumina sintered compact is used in various industrial fields, making full use of the excellent characteristics thereof of high hardness, high strength, high heat resistance, high abrasion resistance, high chemical resistance, etc. In particular, it is used as a starting material (abrasive grain) of heavy grinding stones in steel industry.
Special alloys are being much used as a material for parts constituting transportation equipment centered on automobiles or industrial machinery. These special alloys are hard as compared with ordinary SUS304 and others, and heavy grinding stones heretofore unknown and having a high “grinding ratio” are desired by the market. In this, “grinding ratio” is an index of indicating the performance of grind stones and is represented by the following formula:Grinding Ratio=ground amount of work material(ground amount)/abrasion loss of grind stone
In general, it is considered that a grind stone requiring a smaller amount thereof to grind a larger amount of a work material could have better performance; however, the grinding ratio of a grind stone is influenced by the “hardness” and the “fracture toughness” of the abrasive grains used for the grind stone. It is considered that there would be the following relationships between “the grinding ratio and the hardness”, and “the grinding ratio and the fracture toughness”.
(1) When the hardness of an abrasive grain is high, then the ground amount increases and therefore the grinding ratio becomes high.
(2) When the fracture toughness is high, then the abrasion loss of the abrasive grain reduces and therefore the grinding ratio becomes high.
In consideration of the above (1) and (2), the numerator part in the formula of grinding ratio is influenced by the ground amount, and the denominator part is influenced by the abrasion loss. For increasing the grinding ratio of a grind stone, it is ideal that both the hardness and the fracture toughness thereof are high.
As already-existing abrasive grains for heavy grinding stones, there are known abrasive grains prepared by sintering a fine powder alumina material (for example, see Patent References 1 to 3), molten alumina zirconia abrasive grains (for example, see Patent Reference 4), abrasive grains prepared by adding a crystal grain growth inhibitor such as magnesium oxide or the like to a high-purity fine alumina powder (for example, see Patent Reference 5), etc.
Also proposed is a sintered material comprising aluminium material as the main ingredient and TiO2 added thereto (for example, see Patent Reference 6). Further, as an alumina sintered compact having high hardness and high fracture toughness and excellent in abrasion resistance, proposed is an alumina sintered compact in which a soluble metal compound of Ti, Mg, Fe or the like is added to the alumina crystal (for example, see Patent Reference 7).